0101

0101 is a four-digit binary numeral. In base-2, the bits from most significant to least significant are 0, 1, 0, 1, which equals the decimal value 5. In hexadecimal, the same pattern is 0x05, and in BCD (binary-coded decimal) it can be used to encode the digit 5.

Because binary numbers are often presented in fixed width, leading zeros like the first zero in 0101 are common. Removing the leading zero yields 101, which is a different value and width. This highlights how width affects interpretation in binary notation and digital design.

In practical computing and digital electronics, 0101 is a common test or reference pattern. It alternates bits, making it useful for checking data buses, memory interfaces, and circuit integrity. The pattern is frequently used alongside 1010 to exercise complementary lines and detect stuck-at faults or coupling issues between lines. It also serves as a simple bitmask, where the set bits correspond to positions 0 and 2 in a four-bit vector.

Beyond testing, binary patterns like 0101 appear in programming and hardware configuration as literals, flags, or placeholders for bitwise operations. They help illustrate concepts of bit weighting, masking, and endianness in computer science education.

In summary, 0101 is a small, fixed-width binary pattern valued at 5 in decimal, with practical uses in testing, bit masking, and illustrating binary-width concepts in computing.