Memory organization Flashcards
bit
smallest unit of binary data
byte
8-bit unit
nibbles.
4-bit unit
word
generally, consists of one or more bytes
address
The location of a unit of data in a memory array
two types of memories
Random-Access Memory (RAM),
Read-Only Memory (ROM).
RAM (random-access memory)
is a type of memory in which all addresses are accessible in an equal amount of time and can be selected in any order for a read or
write operation.
ROM (read-only memory)
is a type of memory in which data are stored
permanently or semi permanently
categories of RAM
static RAM (SRAM) and the dynamic
RAM (DRAM)
Static RAMs
generally use flip-flops as storage elements and can,
therefore, store data indefinitely as long as dc power is applied
Dynamic RAMs
It use capacitors as storage elements and cannot retain data very long without the
capacitors being recharged by a process called refreshing.
Comparison between SRAM and DRAM
It consists of a number of flipflops.
Each flip-flop stores one bit.
It stores the data as a charge on the capacitor. It consists of MOSFET and capacitor for each cell.
2
Its access time is less, hence, it is
faster
Its access time is greater than static RAM, hence, it is slower memory
3
It contains less memory cells per unit area. Hence, it is less dense than DRAM.
It contains more memory cells per unit area. Hence, it is denser than SRAM.
4
Refreshing circuitry is not required.
Refreshing circuitry is required to maintain the charge on the capacitors every time after every few milliseconds.
5
It is more expensive than DRAM
It is more expensive than DRAM
6
Power Consumption is lower
Power Consumption is higher
7
Used in cache memory
Used in main memory
8
Occupies more space
Occupies less space
SRAM
DRAM
Types of DRAMs
Synchronous DRAM (SDRAM)
Double Data Rate SDRAM (DDR SDRAM)
Double Data Rate SDRAM (DDR SDRAM)
This memory nearly doubles the bandwidth of a single data rate (SDR) SDRAM
Synchronous DRAM (SDRAM)
The SDRAM synchronizes the speed of the memory along with the CPU clock speed
Classification of ROM
i. Masked ROM (ROM)
ii. Programmed ROM (PROM)
iii. Erasable PROM (EPROM)
iv. Electrically Erasable PROM (EEPROM
Cache Memory
Cache memory holds the data and programs which are frequently used by the CPU
Types of cache memory
L1 cache, or primary cache, is extremely fast but relatively small, and is usually embedded in the processor chip as CPU cache.
L2 cache, or secondary cache, is often more capacious than L1. L2 cache may be embedded on the CPU, or it can be on a separate chip or coprocessor and have a high-speed alternative system bus connecting the cache and CPU
Level 3 (L3) cache is specialized memory developed to improve the performance of L1 and L2. L1 or L2 can be significantly faster than L3,
How does cache work
When CPU needs the data, first of all, it looks inside the L1 cache. If it does not find anything in L1, it looks inside the L2 cache. If again, it does not find the data in L2 cache, it looks into the L3 cache. If data is found in the cache memory, then it is known as a cache hit. On the contrary, if data is not found inside the cache, it is called a cache miss. If data is not available in any of the cache memories, it looks inside the Random Access Memory (RAM). If RAM also does not have the data, then it will get that data from the Hard Disk Drive
Virtual memory
Virtual memory refers to a memory management method where computers use secondary memory to compensate for the scarcity of physical memory
How does virtual memory work
Virtual memory uses both the computer’s software and hardware to work. It transfers processes between the computer’s RAM and hard disk by copying any files from the computer’s RAM that are not currently in use and moving them to the hard disk. By moving unused files to the hard disk, a computer frees up space in its RAM to perform current tasks, such as opening a new application. If the computer later needs to use its RAM for a more urgent task, it can again swap files to make the most of the available RAM
Advantages of virtual memory
Allowing users to operate multiple applications at the same time or applications that are larger than the main memory
Freeing applications from having to compete for shared memory space and allowing multiple applications to run at the same time
Improving efficiency and speed by allowing more processes to sit in virtual memory
Lowering the cost of computer systems as you find the right amount of main memory and virtual memory
