What is the difference between static RAM and dynamic RAM?

2. What is the difference between static RAM and dynamic RAM?

Your computer probably uses both static RAM and dynamic RAM at the same time, but it uses them for different reasons because of the cost difference between the two types. If you understand how dynamic RAM and static RAM chips work inside, it is easy to see why the cost difference is there, and you can also understand the names.

Dynamic RAM is the most common type of memory in use today. Inside a dynamic RAM chip, each memory cell holds one bit of information and is made up of two parts: a transistor and a capacitor. These are, of course, extremely small transistors and capacitors so that millions of them can fit on a single memory chip. The capacitor holds the bit of information -- a 0 or a 1 (see How Bits and Bytes Work for information on bits). The transistor acts as a switch that lets the control circuitry on the memory chip read the capacitor or change its state.

A capacitor is like a small bucket that is able to store electrons. To store a 1 in the memory cell, the bucket is filled with electrons. To store a 0, it is emptied. The problem with the capacitor's bucket is that it has a leak. In a matter of a few milliseconds a full bucket becomes empty. Therefore, for dynamic memory to work, either the CPU or the memory controller has to come along and recharge all of the capacitors holding a 1 before they discharge. To do this, the memory controller reads the memory and then writes it right back. This refresh operation happens automatically thousands of times per second.

This refresh operation is where dynamic RAM gets its name. Dynamic RAM has to be dynamically refreshed all of the time or it forgets what it is holding. The downside of all of this refreshing is that it takes time and slows down the memory.

Static RAM uses a completely different technology. In static RAM, a form of flip-flop holds each bit of memory (see How Boolean Gates Work for detail on flip-flops). A flip-flop for a memory cell takes 4 or 6 transistors along with some wiring, but never has to be refreshed. This makes static RAM significantly faster than dynamic RAM. However, because it has more parts, a static memory cell takes a lot more space on a chip than a dynamic memory cell. Therefore you get less memory per chip, and that makes static RAM a lot more expensive.

So static RAM is fast and expensive, and dynamic RAM is less expensive and slower. Therefore static RAM is used to create the CPU's speed-sensitive cache, while dynamic RAM forms the larger system RAM

3. Write in detail about the dynamic memory allocation.

Dynamic memory allocation

Dynamically allocated memory exists until it is released either explicitly by the programmer, exiting a block, or by the garbage collector. This is in contrast to static memory allocation, which has a fixed duration. It is said that an object so allocated has a dynamic lifetime.

Details

• 
  The task of fulfilling allocation request
  
  • 
    Finding a block of unused memory of sufficient size
    

• 
  Problems during fulfilling allocation request
  
  • 
    Internal and external fragmentation.
    
    • 
      Reduction needs special care, thus making implementation more complex (see algorithm efficiency).
      
  • 
    Allocator's metadata can inflate the size of (individually) small allocations;
    
    • 
      Chunking attempts to reduce this effect.
      

Implementations

Fixed-size-blocks allocation

Main article: memory pool

Fixed-size-blocks allocation, also called memory pool allocation, uses a free list of fixed-size blocks of memory (often all of the same size). This works well for simple embedded systems.

Buddy blocks

For more details on this topic, see Buddy memory allocation.

In this system, memory is allocated from a large block in memory that is a power of two in size. If the block is more than twice as large as desired, it is broken in two. One of the halves is selected, and the process repeats (checking the size again and splitting if needed) until the block is just large enough.

All the blocks of a particular size are kept in a sorted linked list or tree. When a block is freed, it is compared to its buddy. If they are both free, they are combined and placed in the next-largest size buddy-block list. (When a block is allocated, the allocator will start with the smallest sufficiently large block avoiding needlessly breaking blocks)

4. Write about the dynamic translation and paged virtual memory.

Paged virtual memory

Almost all implementations of virtual memory divide the virtual address space of an application program into pages; a page is a block of contiguous virtual memory addresses. Pages are usually at least 4K bytes in size, and systems with large virtual address ranges or large amounts of real memory (e.g. RAM) generally use larger page sizes.

Page tables

Almost all implementations use page tables to translate the virtual addresses seen by the application program into physical addresses (also referred to as "real addresses") used by the hardware to process instructions. Each entry in the page table contains a mapping for a virtual page to either the real memory address at which the page is stored, or an indicator that the page is currently held in a disk file. (Although most do, some systems may not support use of a disk file for virtual memory.)

Systems can have one page table for the whole system or a separate page table for each application. If there is only one, different applications which are running at the same time share a single virtual address space, i.e. they use different parts of a single range of virtual addresses. Systems which use multiple page tables provide multiple virtual address spaces - concurrent applications think they are using the same range of virtual addresses, but their separate page tables redirect to different real addresses.

Paging

Paging is the process of saving inactive virtual memory pages to disk and restoring them to real memory when required.

Most virtual memory systems enable programs to use virtual address ranges which in total exceed the amount of real memory (e.g. RAM). To do this they use disk files to save virtual memory pages which are not currently active, and restore them to real memory when they are needed. Pages are not necessarily restored to the same real addresses from which they were saved - applications are aware only of virtual addresses. Usually when a page is going to be restored to real memory, the real memory already contains another virtual memory page which will be saved to disk before the restore takes place.

Dynamic address translation

If, while executing an instruction, a CPU fetches an instruction located at a particular virtual address, fetches data from a specific virtual address or stores data to a particular virtual address, the virtual address must be translated to the corresponding physical address. This is done by a hardware component, sometimes called a memory management unit, which looks up the real address (from the page table) corresponding to a virtual address and passes the real address to the parts of the CPU which execute instructions. If the page tables indicate that the virtual memory page is not currently in real memory, the hardware raises a page fault exception (special internal signal) which invokes the paging supervisor component of the operating system (see below).

PART-B

UNIT-4

COMPUTER PERIPHERALS

1. Write short notes on hard disk.

Hard Disk (ATA / SATA / SCSI)

�� Used to stored data permanently.

�� Different Type of Hard Disk Size

(3.5”, 2.5”, 1.8”, Micro Drive)

�� Different Interface: ATA / SATA /

SCSI

(Speed: ATA < SATA < SCSI)

�� Different Speed (Mechanical)

(4,200rpm / 5,400rpm /

7,200rpm / 10,000 rpm)

2. Give the details about mother board.
Main Board / Mother Board (MB)

�� Provide a platform to

Connecting all the

Devices.

(Keyboard / Mouse /

Power / CPU /

Memory / Hard Disk /

Floppy Disk / Display

Card etc)

�� Many Main Board has

Already build in Sound

Card / Network Card

Or even display card.
3. Give the details of I/O device and interface.
I/O Device & Interface

�� ATA / SATA /SCSI (For Hard Disk)

�� Parallel Port or LPT Port (For Printer)

�� COM Port (For Modem)

�� RJ45 Socket (For Network)

�� PS/2 (For Keyboard / Mouse)

�� D-Sub / DVI (For Monitor)

�� USB (All compatible devices)

4. Write the details of hard disk memory.
Hard Disk (ATA / SATA / SCSI)

�� Different Build in Memory Size

(2M / 8M / 16M etc)

�� Different Capacity

(80G to 500G or even 1T)

�� Small Size Hard Disk are more popular as

They are portable size.
5. Write short notes on connects of keyboards.

Connection types

There are several ways of connecting a keyboard using cables, including the standard AT connector commonly found on motherboards, which was eventually replaced by the PS/2 and the USB connection. Prior to the iMac line of systems, Apple used the proprietary Apple Desktop Bus for its keyboard connector.

Wireless keyboards have become popular for their increased user freedom. A wireless keyboard often includes a required combination transmitter and receiver unit that attaches to the computer's keyboard port (see Connection types above). The wireless aspect is achieved either by radio frequency (RF) or by infrared (IR) signals sent and received from both the keyboard and the unit attached to the computer. A wireless keyboard may use an industry standard RF, called Bluetooth. With Bluetooth, the transceiver may be built into the computer. However, a wireless keyboard needs batteries to work and may pose a security problem due to the risk of data "eavesdropping" by hackers.^[6]

^{6. What is meant by alternative text entering method?}

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