Page 569 - (ISC)² CISSP Certified Information Systems Security Professional Official Study Guide

periodic basis (see the sidebar “Dynamic vs. Static RAM” for more
information on this subject).

Cache RAM Computer systems contain a number of caches that

improve performance by taking data from slower devices and
temporarily storing it in faster devices when repeated use is likely; this
is cache RAM. The processor normally contains an onboard cache of
extremely fast memory used to hold data on which it will operate. This
can be referred to as L1, L2, L3, and even L4 cache (with the L being

short for level). Many modern CPUs include up to three levels of on-
chip cache, with some caches (usually L1 and/or L2) dedicated to a
single processor core, while L3 may be a shared cache between cores.
Some CPUs can involve L4 cache which may be located on the
mainboard/motherboard or on the GPU (graphics processing unit).
Likewise, real memory often contains a cache of information stored on
magnetic media or SSD. This chain continues down through the
memory/storage hierarchy to enable computers to improve

performance by keeping data that’s likely to be used next closer at
hand (be it for CPU instructions, data fetches, file access, or what have
you).

Many peripherals also include onboard caches to reduce the storage
burden they place on the CPU and operating system. For example,
many higher-end printers include large RAM caches so that the

operating system can quickly spool an entire job to the printer. After
that, the processor can forget about the print job; it won’t be forced to
wait for the printer to actually produce the requested output, spoon-
feeding it chunks of data one at a time. The printer can preprocess
information from its onboard cache, thereby freeing the CPU and
operating system to work on other tasks. Many storage devices, such

as hard disc drive (HDD), solid-state drive (SSD), and some thumb
drives contain caches to assist with improving read and write speed.
However, these caches must be flushed to the permanent or secondary
storage area before disconnection or power loss in order to avoid data
loss of cache resident data.