Browse Definitions :
Definition

Q format

Contributor(s): Matthew Haughn

Q (number) format is a fixed-point method of coding fractional and whole integers for processing by a computer’s CPU or a digital signal processor (DSP).

The Q format is used to enable rational number processing by a standard integer hardware arithmetic logic unit (ALU). Q format is used frequently when a CPU lacks a floating point unit (FPU). The format can also be useful for processing fractions on lower-cost DSPs, reducing hardware costs.

To enable processing of fractions on lower-cost or older hardware, Q is used to imply a binary point to represent fractions. Q format is stored and processed as regular binary signed integer. The Q format specifies how many bits are used to represent whole integers and how many bits are used to represent fractional integers. For example, to note that an algorithm is using one bit to specify whole integers and 15 bits to specify fractional integers, one would use the Q1.15 format. If there is no decimal in a Q format, such as Q55, that implies all bits are used for fractional values.

An example of how a fraction is processed under the Q format would be the real number 5.375 represented as a=0×23+1×22+0×21+1×20+0×2−1+1×2−2+1×2−3+0×2−4=5.375.

The Q format was integral to fractional operations in early PC CPUs. The Intel 8086 was the first CPU to support an add-on floating point co-processor. These co-processors reduced the time spent processing fractions and the need for methods like Q format. Modern CPUs such as the Intel Core series and AMD Ryzen have built-in floating point processors along with the x87 extension on the x86 -64 instruction set.

Watch an introduction to the floating point system below:

This was last updated in January 2018

Continue Reading About Q format

SearchCompliance

SearchSecurity

  • cyber attack

    A cyber attack is any attempt to gain unauthorized access to a computer, computing system or computer network with the intent to ...

  • backdoor (computing)

    A backdoor is a means to access a computer system or encrypted data that bypasses the system's customary security mechanisms.

  • post-quantum cryptography

    Post-quantum cryptography, also called quantum encryption, is the development of cryptographic systems for classical computers ...

SearchHealthIT

SearchDisasterRecovery

  • risk mitigation

    Risk mitigation is a strategy to prepare for and lessen the effects of threats faced by a business.

  • call tree

    A call tree is a layered hierarchical communication model that is used to notify specific individuals of an event and coordinate ...

  • Disaster Recovery as a Service (DRaaS)

    Disaster recovery as a service (DRaaS) is the replication and hosting of physical or virtual servers by a third party to provide ...

SearchStorage

  • cloud SLA (cloud service-level agreement)

    A cloud SLA (cloud service-level agreement) is an agreement between a cloud service provider and a customer that ensures a ...

  • NOR flash memory

    NOR flash memory is one of two types of non-volatile storage technologies.

  • RAM (Random Access Memory)

    RAM (Random Access Memory) is the hardware in a computing device where the operating system (OS), application programs and data ...

Close