Predict: Memory Scenarios

Answer:

Your essay is lost.

The essay was stored in RAM, which is volatile. This means RAM loses all its contents when the power is switched off. Until you save a file, it only exists in RAM. Once saved, it's copied to secondary storage (hard drive/SSD) which is non-volatile.

Answer:

The BIOS stored in ROM tells it what to do.

ROM is non-volatile - it keeps its contents even when power is off. The BIOS (Basic Input/Output System) is stored in ROM and contains the instructions needed to:

1. Test the hardware (POST - Power On Self Test)
2. Find the operating system on the hard drive
3. Load the OS into RAM

Answer:

The computer uses virtual memory.

When RAM is full, the operating system uses virtual memory:

1. Identifies least recently used data in RAM
2. Moves it to a "page file" on the hard drive
3. Frees up RAM for the new program
4. If old data is needed, swaps it back

The computer won't crash, but it will slow down significantly because the hard drive is much slower than RAM.

Answer:

Disk thrashing due to excessive virtual memory usage.

When RAM is severely overloaded, the system constantly swaps data between RAM and the hard drive. This is called disk thrashing:

• Program A needs data → swapped into RAM
• Program B needs its data → A's data swapped out
• Program A needs data again → B's data swapped out
• This cycle repeats constantly

Solution: Close programs, or add more RAM to the computer.

Answer:

Cache saves approximately 98,000 nanoseconds (98 microseconds).

Cache is roughly 100× faster than RAM, making it crucial for performance. Even though cache is tiny compared to RAM, a high "hit rate" makes a huge difference.

Answer:

Modern computers use EEPROM or Flash ROM.

Traditional ROM truly couldn't be changed. However, modern "ROM" is usually:

• EEPROM (Electrically Erasable Programmable ROM) - can be rewritten with special software
• Flash ROM - similar to EEPROM, easier to update

We still call it "ROM" because:

• It's non-volatile (keeps data without power)
• It's not meant for regular writing
• Updates are rare (unlike RAM which changes constantly)

Answer:

Computer B (SSD) will perform much better.

Virtual memory requires reading and writing to secondary storage. SSDs are much faster than HDDs:

Storage Type	Typical Speed
HDD	100-200 MB/s
SSD (SATA)	500-600 MB/s
SSD (NVMe)	3,000-7,000 MB/s

This is why upgrading to an SSD makes such a noticeable difference, especially on computers with limited RAM.

Answer:

The data will come from virtual memory (hard drive). This is a "page fault".

When data isn't in RAM, it must be in the page file on secondary storage. The OS must:

1. Find the data in the page file
2. Load it into RAM (possibly swapping something else out)
3. Then the CPU can access it

This is called a page fault - not an error, but it causes significant delay.

Answer:

Option B (16GB RAM) would be much better.

Virtual memory is NOT equivalent to RAM:

• RAM is approximately 100,000× faster than an HDD
• Even with an SSD, RAM is still 100× faster
• Games need fast, constant access to data
• Virtual memory causes stuttering and lag

16GB of real RAM means the game can run entirely from fast memory, avoiding slow virtual memory access.

Answer:

The phone closes background apps automatically.

Unlike computers, most smartphones don't use virtual memory because:

• Flash storage has limited write cycles
• Constant writing would wear out the storage
• Battery life would suffer

Instead, the OS uses "app killing":

• Monitors RAM usage
• When full, closes least-recently-used apps
• Apps reload when you switch back to them