SPARC (Scalable Processor Architecture) Explained

What is SPARC (Scalable Processor Architecture)

What is SPARC (Scalable Processor Architecture)?

SPARC, or Scalable Processor Architecture signifies the structure of a RISC or Reduced Instruction Set Computer microprocessor. In theory, this architecture includes a scalar CPU.

Technically, this is an open architecture that is highly scalable and offers quick execution rates.


  • Scalable Processor Architecture was originally developed in 1987 by Sun Microsystems and is available in a wide variety of computers.
  • SPARC is usually recognized with the Solaris operating system and is designed to optimize both 32-bit as well as 64-bit implementations.
  • There are three basic parts of the SPARC processors such as an Integer Unit, a Floating-Point Unit, and an optional coprocessor. Each of these units comes with its own 32-bit wide registers.
  • These specific types of processors can operate in two typical modes such as supervisor mode and user mode.
  • With continual development made to this architecture over the years, SPARC is available in different versions such as a 32-bit SPARC-V7, a 32-bit SPARC-V8, a 64-bit SPARC-V9, and an extension of SPARC-V9 in UltraSPARC.

Understanding Scalable Processor Architecture (SPARC)

What is SPARC (Scalable Processor Architecture)

SPARC stands for Scalable Processor Architecture and signifies a general purpose Instruction Set Architecture based on RISC design.

It is also referred to as a 32, 64, and 128-bit floating-point unit or a 32-bit integer.

Typically, the SPARC processors can operate in two specific modes such as:

  • Supervisor mode – Here the CPU executes any instruction which may even be a privileged instruction.
  • User mode – All the user applications are executed in the user mode.

After its launch in 1987, a lot of revisions have been made on the SPARC architecture design by Sun Microsystems with additions of newer features.

For example, the version 8 of this architecture includes functionalities like multiply and divide and features such as a 128-bit quad-precision register.

In the following years, the notable improvements made on the design of this architecture and its different versions are as follows:

  • SPARC-V7, a 32-bit architecture
  • SPARC-V8, a 32-bit architecture
  • SPARC-V9, a 64-bit architecture
  • UltraSPARC, an extension of SPARC-V9

Typically, the term ‘scalable’ in SPARC signifies the register stack which can be scaled up to 512 or up to 32 windows. This helps in minimizing workloads on the processor.

On the other hand, when required, the register can even be scaled down. This will help in minimizing the time taken to switch context or interference in the process or cores.

Ideally, the register plays a very important role in this specific type of architecture.

During a function call, the window is passed down the stack by 16 registers at some point in time. This helps in sharing the lower and upper registers between the functions.

This window can be pushed up again when needed, which in turn will push the local registers to the top or bottom of the stack.

This specific feature allows maintaining the local values across function calls.

Designed and developed by Sun Microsystems, the SPARC architecture is usually associated with the Solaris operating system of their own.

However, in addition to that, the design of this scalar processor also supports other operating systems such as:

  • SunOS
  • OpenSolaris
  • NetBSD
  • OpenBSD
  • Linux and others

What are the Three Modules in the SPARC Processor?

There are typically three modules of the SPARC processor, such as the Integer Unit (IU), the Floating-Point Unit (FPU), and the optional Coprocessor (CP).

Each of these modules has its own registers that are typically 32-bits wide and performs respective functions that are controlled by the integer unit.

The Integer Unit

The IU is made up of several 32-bit wide general purpose registers, ranging anywhere between 40 and 520.

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It typically corresponds to a set of 8 universal registers and a circular stack. This stack is usually 2 to 32 sets of 16 registers and is normally called the register windows.

The IU manages the overall functioning of the processor. It is also used for several other purposes such as:

  • Executing integer arithmetic instructions
  • Computing memory addresses for loads and stores
  • Maintaining program counters
  • Controlling instruction execution for both the CP and FPU

The Floating-Point Unit

The FPU is typically made up of 32 registers that are 32 bits wide. The values occupied by these units are quite different as follows:

  • The double-precision values typically occupy an even-odd pair
  • The extended-precision values usually occupy an arranged group of four registers.

These registers allow only external accessibility with the help of the load and store instructions. There is usually no direct path that connects the FPU and the IU.

The Coprocessor

The instructions of the CP typically mirror the instructions of the floating point and typically execute instructions at the same time as with integer instructions.

The coprocessor unit, which may have branches on coprocessor condition codes, load/store coprocessor, and coprocessor operate or CPop, usually comes with its own set of 32-bit registers.

However, the real design of the registers is typically dependent on the implementation.

Is SPARC Open Source?

Typically, OpenSPARC is open-source hardware. The UltraSPARC T1 processor was released in March 2006 in an open-source form and was called OpenSPARC T1.

It is a large piece of hardware and with a more complex design where a complete microprocessor is in open-source form.

This is much unlike that tiny, open-source computer hardware IP with circuit descriptions typically written in an RTL or Register Transfer Level language such as VHDL or Verilog.

Its successor, OpenSPARC T2, was also released in early 2008 in open-source form.

Both of these are the first, and probably the only, 64-bit, open-source CMT or Chip Multithread processors.

Both these open-source designs have comprehensive source codes which include millions of lines of the hardware description language such as Verilog for the microprocessors.

In addition to that, there are also scripts available to synthesize or compile the source code and put it into several hardware implementations.

That is not all. These freely available processors come with several features which include the following:

  • The design source code
  • Simulation and other useful tools
  • Hypervisor software layer source code
  • Full system simulators
  • Prepackaged images of the operating system for booting on the simulators
  • Thousands of pages of structural design
  • Implementation pattern documents
  • Design verification software suites

You will also get variants that can be synthesized easily for the FPGA or Field Programmable Gate Array targets.

An OpenSPARC has different significance for different users, for example:

  • To a developer, the source codes allow for the creation of inventive and optimized software applications in quick time. It also allows a superior degree of hardware integration of both that eventually allows creating high-value and unique solutions for particular market segments.
  • To an EDA developer, this offers a platform for testing and demonstrating the capabilities of the tools that are to be used for commercial designs.
  • To a professional or a learner, the source codes of both of these processors offer them an opportunity to test, research, create or modify unique solutions based on a tried and tested architecture.

Therefore, open-source SPARC is a platform that allows collaboration in chip design and boots commonly used commercial operating systems such as Solaris, FreeBSD, and Linux.

Apart from that, it also helps in VLSI or Very Large Scale Integration design methodology innovations.

Can You Run Linux on SPARC?

Yes, you can run several distros of Linux since these are well supported by the SPARC hardware. Moreover, the source code of Linux is developed under the GNU General Public License and is available freely for anyone to use.

In fact, SPARC supports a variety of operating systems apart from Linux such as:

  • OpenBSD
  • FreeBSD
  • NetBSD
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However, it does not support Windows NT though Intergraph announced a port for it in 1993, which was cancelled later.

What are the Features of the SPARC Architecture?

Some of the most notable features of the SPARC architecture include its high scalability of the register stack, faster execution rates, and an open architecture.

Some other noteworthy features of this architecture are:

  • Higher performance and economy, which are due to its larger number of disentangled instruction sets with fewer transistors
  • Higher adaptability in terms of cost, capacity, and incorporation of memory, cache and FPUs
  • Full compatibility from one generation to another of the structure is offered, offering options to use the full scope of items on each SPARC implementation
  • More versatility in terms of applications which include technical, commercial, military, aerospace and more
  • More dominant object-oriented programming features
  • Based on the RISC design
  • Large number of general purpose registers
  • The 32-bit RISC architecture has a 32-bit wide register bank
  • Register windowing that supports context switching, parameter passing, and superscalar operations
  • 15 external interrupts support
  • The level 15 is assigned for a nonmaskable interrupt and the other 14 levels of the processor are unmasked but can be made maskable if needed
  • 64 instructions of the instruction set of a SPARC processor with a RISC architecture are accessible by load and store operations
  • Internal trap generated in the trap base register when external interrupt is generated, which saves the current and following instructions, and the processor turns into the supervisor mode and the pipeline is flushed
  • A trap vector table located in the trap base register that supplies the service routine address, and when it is completed, the REIT instructions are carried out
  • Three modules namely IU, FPU and CU or CP
  • 32 single precision floating registers of 32 bits, 32 double precision floating registers of 64 bits, and 16 quads precise floating registers with 128 bits
  • IU containing all the General Purpose Registers or GPRs

How Many Registers Does SPARC Have?

Usually there are as many as 160 General Purpose Registers in the SPARC processor. The implementation may be different according to the SPARC architecture specification and in some cases it may contain anywhere between 72 and 640 GPRs of 64 bits.

Ideally, at any given point in time, only 32 of these registers are visible to the software program immediately.

Eight of the registers are a set of global registers, out of which one is hardwired to 0. This means that seven of these eight are only usable as registers.

The other 24 registers form the stack registers which consist of:

  • In registers
  • Out registers
  • Local registers

These 24 stack registers are called a register window. This widow is moved up or down the stack during a function call or return.

Every such window consists of 8 local registers. 8 registers are shared with each of the neighboring windows.

These shared windows help in passing the function parameters and the returning values. On the other hand, the logical registers are utilized to keep hold of the local values over the function calls.

On the other hand, in the SPARC Version 8, there are 16 double-precision registers in the floating-point register file.

Each of these double-precision registers can be utilized as two single-precision registers. This means that you will have as many as 32 single-precision registers at your disposal.

However, if the double-precision registers are an odd-even number pair, they can act as a quad-precision register. This means that you will have eight quad-precision registers.

On the other hand, in the SPARC Version 9, there are 16 more of these double-precision registers added.

These registers are accessible as eight quad-precision registers, but the added registers are not accessible as single-precision registers.

In a SPARC implementation, the number of windows can range anywhere between 2 and 32. This means that the number of registers can add up to anywhere between 40 and 520.

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However, in most implementations, there are only 7 or 8 windows available, and at any given time, one of these windows is perceptible and determined by the CWP or Current Window Pointer, which is an element of the Processor Status Register or PSR.


  • A simple and quite powerful processor architecture
  • A more advanced structure
  • Loads of useful and high-performing features
  • Support for real-world applications
  • Low Cost of Ownership
  • High productivity per center
  • Expanded adaptability and flexibility
  • Higher scalability
  • Better and higher levels of accessibility
  • Reduced CPU waste time
  • Better CPU usage


  • Cannot be morally used for educational purposes
  • Suitable for use only by the computer architects and developers
  • Supports low level programming and server applications only
  • Higher chances of misuse being an open architecture

SPARC vs x86

  • SPARC processors can perform much better and can do more in a short amount of time as compared to the x86 processors.
  • SPARC architecture is supposed to be relatively expensive in comparison to the x86 architecture.
  • The SPARC architecture scales out much better in comparison to the x86 architecture.
  • The SPARC architecture is designed to run more threads and support 8-way systems, but, in comparison, the x86 architecture lags behind it in these specific aspects.
  • A large number of jobs can be performed by the SPARC processors, but, in comparison, the x86 processors cannot handle large volumes  of jobs.
  • The Database software performance is superior in a SPARC box as compared to that in an x86 box.
  • The SPARC platform is much more stable in comparison to the x86 platform.
  • The downtime is less in the case of SPARC architecture as compared with the operational downtime in x86 architecture.
  • The SPARC processors are much more power efficient when compared to the power efficiency aspect of the x86 processors.
  • In terms of single threaded performance, it is however better in the case of x86 processors than in the case of the SPARC processors.
  • In the SPARC processors the hardware architecture is different from that of the x86 processors.
  • The number of cores in the SPARC processors is higher, but in comparison, the x86 processors come with fewer but beefy cores.
  • The SPARC processors are basically throughput-oriented and deliver higher throughput in aggregate as compared to the x86 processors that are typically latency-oriented.
  • The compiler options in the SPARC architecture and that in the x86 architecture are different, which means that those available in SPARC are not available in x86, and vice versa.
  • The instruction set and their applications of SPARC are quite different and compact than the instruction sets of x86 architecture.
  • The SPARC processor performs well on a narrow range of database workloads, but, in comparison, the x86 processors can perform well across a wider range of workloads.
  • The SPARC is basically a legacy architecture and may stick to the Oracle world, but in comparison, x86, especially x86-64, is more of a dominant desktop and server architecture.

What is SPARC Used for?

The design of SPARC which is based on RISC makes it quite a useful architecture for hardware that is typically used with operating systems based on UNIX, including the Solaris operating system of Sun Microsystems, the creator of SPARC architecture.

Several microprocessor manufacturing companies also use this to implement in their products.

It is good to use for writing low-level codes for parallel processing.


The SPARC processors, just like the ARM processors, are based on the RISC architecture.

This makes them quite different from the x86 architecture, which is based on CISC or Complex Instruction Set Computer.


The SPARC architecture is influenced by the RISC system and its features and success resulted in more RISC designs from several vendors in the course of the 1980s and 1990s.

The architecture offers high performance and the processors allow for better system implementations at a wide range of technology points.

About Taylor

AvatarTaylor S. Irwin is a freelance technology writer with in-depth knowledge about computers. She has an understanding of hardware and technology gained through over 10 years of experience.

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