1.2 Memory & Storage

1.2 Memory & Storage

1. Primary Storage & Virtual Memory

   • ROM: Non-volatile, stores boot-up sequence & operating system, as you don't want to lose it when you power off computer. ROM is read only.
   • RAM: Volatile, stores currently running apps. RAM is read and write.
   • Virtual Memory: When RAM is full, part of secondary storage is used as 'virtual memory', acting as an extension of RAM.

2. Secondary Storage

   • Magnetic: Cheaper per GB, large capacity, relatively fast read or write. However, it is loud, has moving parts, and isn't portable.
   • Solid State: Its expensive per GB. On the other hand, it is durable (no moving parts), portable, large capacity, small in physical size, fast read and write speeds.
   • Optical: Cheapest and small / portable, but easily damaged, limited capacity and has slow read and write speeds.

3. Characters Sets & Images

   • ASCII: 7 bits (8 bits is extended). Only represents English characters. 128 characters total, or 256 extended.
   • Unicode: 16 bits, many languages included. Emojis also included. Total of 65,536 characters.
   • Bitmap Images: Made up of pixels, each pixel having a colour represented via binary. Eg. 8 total colours = 000, 001, 010, etc. or 3 bits total.
   • Metadata: Data about data - eg. file size of an image, where the image was created / taken, etc.

4. Sound & Compression

   • 1. Amplitude of wave is measured.
   • 2. Amplitude is then measured at set intervals - known as the sample rate.
   • 3. The amplitude is then converted to binary.
   • Lossy Compression: Cannot go back to the original file. Removes unnecessary data. This is for image, sound and video files. Cannot be used on text files.
   • Lossless Compression: Can go back to the original. File size does not decrease that much, and useful for (usually only) text files.